[PATCH] fbmem: Reject FB_ACTIVATE_KD_TEXT from userspace

[Maarten Lankhorst]

On 2023-04-11 15:44, Daniel Vetter wrote:
> On Tue, Apr 04, 2023 at 09:39:34PM +0200, Daniel Vetter wrote:
>> This is an oversight from dc5bdb68b5b3 ("drm/fb-helper: Fix vt
>> restore") - I failed to realize that nasty userspace could set this.
>>
>> It's not pretty to mix up kernel-internal and userspace uapi flags
>> like this, but since the entire fb_var_screeninfo structure is uapi
>> we'd need to either add a new parameter to the ->fb_set_par callback
>> and fb_set_par() function, which has a _lot_ of users. Or some other
>> fairly ugly side-channel int fb_info. Neither is a pretty prospect.
>>
>> Instead just correct the issue at hand by filtering out this
>> kernel-internal flag in the ioctl handling code.
>>
>> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
>> Fixes: dc5bdb68b5b3 ("drm/fb-helper: Fix vt restore")
>> Cc: Alex Deucher <alexander.deucher at amd.com>
>> Cc: shlomo at fastmail.com
>> Cc: Michel Dänzer <michel at daenzer.net>
>> Cc: Noralf Trønnes <noralf at tronnes.org>
>> Cc: Thomas Zimmermann <tzimmermann at suse.de>
>> Cc: Daniel Vetter <daniel.vetter at intel.com>
>> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>> Cc: Maxime Ripard <mripard at kernel.org>
>> Cc: David Airlie <airlied at linux.ie>
>> Cc: Daniel Vetter <daniel at ffwll.ch>
>> Cc: dri-devel at lists.freedesktop.org
>> Cc: <stable at vger.kernel.org> # v5.7+
>> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie at samsung.com>
>> Cc: Geert Uytterhoeven <geert at linux-m68k.org>
>> Cc: Nathan Chancellor <natechancellor at gmail.com>
>> Cc: Qiujun Huang <hqjagain at gmail.com>
>> Cc: Peter Rosin <peda at axentia.se>
>> Cc: linux-fbdev at vger.kernel.org
>> Cc: Helge Deller <deller at gmx.de>
>> Cc: Sam Ravnborg <sam at ravnborg.org>
>> Cc: Geert Uytterhoeven <geert+renesas at glider.be>
>> Cc: Samuel Thibault <samuel.thibault at ens-lyon.org>
>> Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
>> Cc: Shigeru Yoshida <syoshida at redhat.com>
> An Ack on this (or a better idea) would be great, so I can stuff it into
> -fixes.
Acked-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>